ALBUQUERQUE, N.M. — Facing heat from Democrats, Senator McCain used a Memorial Day appearance to defend his opposition to Senate-passed legislation that would provide additional college financial aid to veterans.

The issue has become a point of contention between the Republican nominee in waiting and Democratic rival Senator Obama, who supports the measure. The two have squared off from a distance in recent days, at times with heated words.

In his remarks today, Mr. McCain made no direct mention of Mr. Obama but seemed to poke at him nonetheless. Mr. McCain said his was the right position rather than the politically expedient one, suggesting Mr. Obama was on the wrong side of the measure sponsored by Senator Webb, a Democrat of Virginia.

Last week, the Democratic-controlled Senate approved the bill, which would substantially increase educational benefits for service members returning from Iraq and Afghanistan. Lawmakers blocked a more limited version that Mr. McCain supported.

“I am running for the office of commander in chief. That is the highest privilege in this country, and it imposes the greatest responsibilities. And this is why I am committed to our bill, despite the support Senator Webb’s bill has received,” Mr. McCain, a Navy veteran and Vietnam prisoner of war, said at the New Mexico Veterans Memorial. “It would be easier, much easier politically for me to have joined Senator Webb in offering his legislation.”

“More importantly, I feel just as he does, that we owe veterans the respect and generosity of a great nation because no matter how generously we show our gratitude it will never compensate them fully for all the sacrifices they have borne on our behalf,” the Arizona senator said.

However, Mr. McCain said he opposed Mr. Webb’s measure because it would give the same benefit to everyone regardless of how many times he or she has enlisted. He said he feared that would depress reenlistments by those wanting to attend college after only a few years in uniform. Rather, Mr. McCain said the bill he favored would have increased scholarships based on length of service.

On Saturday, Mr. Obama told veterans while campaigning in Puerto Rico: “I don’t understand why John McCain would side with George Bush and oppose our plan to make college more affordable for our veterans. George Bush and John McCain may think our plan is too generous. I could not disagree more.”

Mr. McCain said today: “I take a back seat to no one in my affection, respect, and devotion to veterans.”

Both Messrs. McCain and Obama both were spending part of the holiday in New Mexico, a general election battleground decided by razor-thin margins in 2000, for the Democratic candidate, and in 2004, for the Republican. Mr. Obama had scheduled a meeting with veterans in Las Cruces, in the southern part of the state.

Mr. McCain spent the early part of the holiday weekend at his retreat in Sedona, Ariz., where he entertained some two dozen guests, including three fellow Republicans who have been mentioned as possible vice presidential candidates: Governor Crist of Florida, Governor Jindal of Lousiana and the former Governor of Massachusetts, Mitt Romney.